Multi-terabit routers in communications networks currently use electrical crossbar switching fabrics to perform switching of electrical packets between line cards in routers having a capacity of tens of terabits per second or more. The limited number of ports in the switch elements of the switching fabric means that complex switching fabrics comprising many switch elements are required in order to provide the required routing capacity. Such high capacity routers typically consist of a multi-rack hardware configuration comprising many line card racks and switch fabric racks. While this type of hardware configuration can be used to construct large capacity switch fabrics, they have high power consumption and a large footprint, both of which scale rapidly to unacceptable levels as the switch capacity is increased.
Various solutions for routing in optical communications networks have been proposed based on all-optical routing, so that no conversion into the electrical domain is required. R. S. Tucker, “Optical Packet Switching: A Reality Check”, Optical Switching and Network Volume 5, 2008, reports various optical switch fabrics for all-optical packet switched applications, including an optical switch fabric comprising rapidly tunable wavelength converters and arrayed waveguide gratings.